The present invention relates to three-dimensional imaging and more particularly to autostereoscopic imaging.
Three-dimensional (3D) imaging relies on the human ability to receive two dissimilar images of the same object simultaneously and thus perceive depth. The image projections for stereo or binocular viewing have not changed since Euclid's description in 280 A.D.; however, technologic and photographic advances have made it easier to produce the two images that stimulate the eye's binocular parallax and convergence cues. The power and flexibility of computer graphic tools and techniques facilitates the creation of stereoscopic images.
The stereoscope was developed in the 1800's by Niepce, Wheatstone, Brewster and Holmes, but major achievements in and public awareness of 3D imaging did not occur until the 1900's. Stereocameras that produced binocular picture information were developed, some of which are still available today, and related technologies evolved from Kennedy, Kanolt, Lippmann and Ives. The technologies explored were the parallax barrier, chromolinoscope, panoramagram, and integral fly's-eye and lenticular photography. By the mid 1900's anoglyphic and polarized 3D movies had been developed. Cinerama and holography retained public interest, with work being done throughout the world in autostereographic television and lenticular-sheet 3D pictures. Advancements to lenticular-sheet imaging were made by scientists Vanbenschoeten, Bonnet and Winnek, and by industries, including Eastman Kodak and Japan's Toppan and Dai-Nippon printing companies.
One form of stereography, based on parallax barriers, is carried out in the chromolinoscope and panoramagram that are described in U.S. Pat. Nos. 666,424 and 725,567, and in H. E. Ives, "The Chromolinoscope Revived," J. Oct. Soc. Amer. 20, pp. 343-353 (June 1930) and H. E. Ives, "A Camera for Making Parallax Panoramagrams," J. Opt. Soc. Amer. 17, pp. 435-439 (Dec. 1928). Other forms of stereography are described in B. Jequier, "Some Simple Means of Realizing 3D Images with Standard Material in Diverse Fields of Medicine, Industry and Research," Proceedings of the SPIE No. 402/37, Geneva (1983), S. H. Kaplan, "Theory of Parallax Barriers," J.SMPTE 59, No. 7, pp. 11-21 (July 1952), and T. Okoshi, Three-Dimensional Imaging Techniques, Academic Press, New York (1976).
As illustrated in FIG. 1, the parallax barrier or barrier strip method cuts a predetermined number of different views of an object into vertical columns (oriented perpendicular to the plane of the Figure), interleaves the columns on a film or transparency 11, and positions them behind the slits of a barrier strip or line screen 12 that is fixed at a predetermined position with respect to the film 11, for example by a transparent spacer 13. Strips 11-1 thru 11-5 of five different 2D or planar views are interleaved in FIG. 1. The position of the eye 14 determines what view the observer sees, five eye positions 14-1 thru 14-5 being shown, and in this way a truly spatial image, i.e., one which gradually shows its right side when the observer moves leftward and its left side when the observer moves rightward, can be perceived. Such a spatial image is sometimes called an autostereogram when more than two different views of the object are interleaved to distinguish it from a binocular or stereoscopic image.
Many 3D photographers today use Bonnet-style cameras which include barrier strips. In these devices it is the camera which interleaves or combines the several views. In a one-step dedicated process, they photograph a scene, and the barrier strip is immediately imposed on the film during processing in the camera. The images produced have a predetermined spatial frequency (also referred to as pitch, in lines per inch) and can only be magnified proportionally. As a result, images that are reduced or magnified may appear too fine or too coarse. Using a two-step combining process expands the photographer's flexibility to magnify or crop images. For example, a Jequier-type projection system uses a given number of different negatives of an object scene, previously photographed on negative film from that number of different positions. Each negative is inserted, in sequence, in a movable stage that slides left and right; the recording film and barrier strip move accordingly. The system thus splits an image into vertical columns, interleaves them and records them on film.
Another camera-combining process is the Cunnally projection system which uses a movable barrier strip with the rest of the system remaining stationary. The barrier strip moves 1/n-th the distance between barrier strip lines for each of the n slides to be interleaved. The film recording the interleaved images is placed on a vacuum-backed table; the barrier strip is mounted in a frame which is attached to the table with spring-loaded pins. A micrometer is used to control the movement of the barrier strip with a precision up to 1/000-th of an inch.
Yet another image combining process in which a camera combines the images is the Illusion projection system which photographs n different scenes off a CRT screen. The lens and the CRT monitor move n proportional distances left and right; the film and barrier strip remain fixed. This process splits each image into vertical columns, interleaves them, and records them on film.
Other camera-based methods and apparatus for making 3D images are disclosed in U.S. Pat. Nos. 1,600,297; 4,596,458; 4,557,954; 4,481,050; 4,158,501 and 1,260,682, and in R. P. Guzik, "Current Technology in 3-D Electronic Displays," Electronic Imaging '88, Anaheim, Calif. (Mar. 30, 1988), A. Ortony, "A System for Stereo Viewing," The Computer Journal vol. 14, no. 2, pp. 140-144 (May 1971).
The inaccuracies and inflexibilities associated with the camera-combining techniques have, however, been a constant source of problems. Cameras are subject to geometric changes with temperature and humidity, exposure problems and color balance problems. The process itself is expensive and slow because of many processing steps, requires a large physical facility for camera, darkroom, and so on, and depends upon outside assistance for photoprocessing. Furthermore, camera-combining autostereography equipment is generally not very portable, and requires image subjects to be brought to a studio and to be motionless for long periods because of the large formats and small lens apertures they require. Because much of the imaging effort involved is already computer-based, using a computer to do the combining, thereby eliminating the photographic process altogether, has important advantages for stereography.